Not a solution, but some related information for you. . .
 
 I' m also using FSAE with edirectory.  The FSAE agent tends to give off errors on the server.  Don' t know why.  Have not been able to solve.  Others have reported the same issue (search forums for fsae), but seems to continue to function OK.
 
 I don' t use non-authenticated guest access, so have not seen the issue you' ve mentioned.  Guest users need a guest password for a web login on my network. 
 
 What firmware and FSAE version are you using?
 
 Once authenticated, the Fortigate needs to periodically re-authenticate the user if it hasn' t seen any traffic from that user.  If that re-authentication fails, my guess is that it reverts security to Guest (unauthenticated).
 
 The trick is to find out why the re-authentication is failing.
 
 My advice would be to change your authentication timeout temporarily to something like 2 hours to see if that has any affect.  If so, then at least you' ll know you' re on the right trail.
 
 The setting is in User|Options.
 
 If it' s any help, you can also use the CLI to set specific timeouts for different groups.  My guest logins reauthenticate every 15 minutes.  But my FSAE logins are much longer -- typically just people logging in for the day at their own desktops.  No need to constantly reauthenticate those.
 
 Bill
					
				
			
			
				
	Bill
 
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 Fortigate 600C 5.0.12, 111C 5.0.2
 Logstash 1.4.1